Heat retaining sheet

ABSTRACT

This invention relates to a heat retaining sheet comprising at least a web in which fibers containing polybutylene terephthalate as at least one of their components and having a substantially undrawn definite fiber length are mutually bonded, and which has small area shrinkage in boiling water. The present invention provides a heat retaining web which is particularly useful as the heat retaining material for batting or interlining for clothing, gloves, hats, bedclothes and so forth.

FIELD OF THE INVENTION

This invention relates to a heat retaining sheet and more particularly,to a heat retaining sheet useful as a heat retaining material forbatting or interlining in clothing, gloves, hats, bedblothes and thelike.

BACKGROUND OF THE INVENTION

As heat retaining sheets, batting and quilted materials formed by sewingthe batting with fabric having conventionally been known. To improve theheat retaining properties of clothes by the use of heat retaining webs,it has been necessary to increase the thickness of the heat retainingsheet or to increase its apparent density at the sacrifice of thedrapability and functionality of the clothes when the clothes are worn,resulting in an unattractive appearance of the clothes. Hence, theapplication of the heat retaining sheet has been limited to clothes foruse in cold weather such as ski wear.

To solve this problem, Japanese Patent Laid-Open No. 41577/1978, forexample, proposes a web of undrawn micro-fibers formed by melt-blowingpolyethylene terephthalate, polyamide or polypropylene. However, thenon-woven web consisting of polyethylene terephthalate exhibits largearea shrinkage in boiling water, generally scoring a value of at least60%. When the heat retaining material is worn for an extended period oris washed repeatedly, problems such as creasing and breakage of yarnsare likely to occur due to the difference in shrinkage between the weband various woven or knitted fabrics attached to the surface thereof. Inthe case of the non-woven web of fibers consisting of polyamide,recovery of compressive elasticity is generally 50% or less and bendingrigidity is poor. In addition, it has poor washability because shrinkageduring washing is as large as 10%. On the other hand, non-woven fabricconsisting of a low heat-resistant polymer such as polypropyleneundergoes shrinkage or is fused with the resulting lowered elasticrecovery when subjected to various operations for clothes, such aspressing. If exposed to a high temperature environment for an extendedperiod, for example, at 150° C. for 1.5 hour, the web suffers from acritical drawback in that autogenous ignition occurs.

On the other hand, as an attempt to impart stretchability to thenon-woven web, it has been known to employ an elastic adhesive or fiber.

When an elastic adhesive is used, however, adhesion between the web andthe adhesive is not sufficient and surface destruction occurs when theweb is stressed. Also a sufficient stretch recovery properties can notbe obtained.

As a method for using elastic fibers, Japanese Patent Laid-Open No.16910/1980 discloses a method wherein an elastic film containing afoaming agent is expanded and then stretched to obtain a web having areticular non-woven structure. Since, however, the fiber structure ofthis reticular web is formed by stretching after expansion, the fiberstructure is strongly bundled in the stretching direction and since thesize of the fibers is great and the fibers are not sufficientlyseparated and independent, flexibility is insufficient.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a thin heatretaining sheet which is devoid of the above-mentioned problems,maintains essentially the feel, appearance and other properties of thebase materials, insures functionality of clothes when worn and providesexcellent heat retaining properties.

It is another object of the present invention to provide a heatretaining sheet for industrial use having excellent durability and heatretaining properties.

It is still another object of the present invention to provide a heatretaining sheet which neither exhibits creases nor deforms but can becleaned by dry cleaning and laundering and is free from inflammability.

It is still another object of the present invention to provide anelastic sheet which has a high heat retaining properties, is very softand flexible and has an especially high stretch recovery ratio.

These objects of the present invention can be accomplished by a heatretaining web consisting of webs in which fibers containing polybutyleneterephthalate as at least one of the components and having asubstantially unstretched definite fiber length are mutually bonded, andwhich have area shrinkage when treated with boiling water of up to about20%.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing an example of the production methodof the heat retaining web in accordance with the present invention;

FIGS. 2 and 3 are schematic perspective view and schematic partiallyenlarged sectional view, each showing an example of the heat retainingweb in accordance with the present invention;

FIGS. 4 and 5 are scanning electron micrographs, each showing thesurface condition of the heat retaining web of the present invention;

FIG. 6 is a schematic perspective view showing another example of theheat retaining web of the present invention; and

FIGS. 7 and 8 are schematic plan views, each showing an example ofclothes using the heat retaining web of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Of THE INVENTION

Hereinafter, the heat retaining sheet of the present invention will bedescribed in detail.

The heat retaining sheet of the present invention consists of at least aweb in which fibers containing polybutylene terephthalate as at least apart of the fiber-forming components and having a substantially definitefiber length are mutually bonded, and which have area shrinkage inboiling water of up to about 20%.

Namely, the web forming the heat retaining sheet of the presentinvention is composed of fibers of a definite length consisting ofnon-continuous filaments and containing polybutylene terephthalate as atleast one of the fiber-forming components. The fibers consist ofunstretched yarns but not of stretched yarns, whereby the unstretchedyarns are independent of, and separated from, one another withoutforming bundles, and are laminated while being kept sufficiently opened,thus forming thin layers. These thin layers are in turn layered likescales, thereby forming the non-woven web. The points of contact betweenthe constituent fibers are melt-adhered and entangled by the fibers bythemselves.

In order to obtain a heat retaining web having high heat retainingproperty, and being excellent in dimensional or shape stability and softand rich in draping properties in accordance with the present invention,it is important to use, as the fiber raw material, polybutyleneterephthalate or a copolymer type polybutylene terephthalate obtained bycopolymerizing polybutylene terephthalate with small amounts ofcomonomers such as isophthalic acid, adipic acid, phthalic acid orsebacic acid, and to keep the area shrinkage of the web in boiling waterat about 20% or below.

In the heat retaining web of the present invention, it is preferred thatthe area shrinkage of the web in boiling water be below about 20%, theaverage fineness of the web-forming fibers be up to 15 d and thefineness distribution be within the range of 0.001 to 40 d. If theaverage fineness is 15 d or below, there can be obtained a heatretaining web having sufficiently high heat retaining properties andhigh wash resistance. To obtain a heat retaining web which is thin andyet has high heat retaining properties, the average fineness is as lowas possible and up to about 0.5 and preferably from 0.03 to 0.5 d, andthe fineness distribution is from 0.01 to 1 d. To obtain good washresistance, it is advisable to set the average size at a considerablylarge value. The fineness condition is preferably selected in accordancewith the intended application or object.

In addition to the requirements for the predetermined area shrinkage inboiling water treatment and the fineness requirements, the heatretaining web according to the present invention preferably satisfiesthe requirement that the web has an apparent density of up to about 0.1g/cm³, preferably, from 0.01 to 0.1 g/cm³. If these conditions aresatisfied, there can be obtained a heat retaining web having a thermalinsulation value of as high as at least 1.8 clo/cm.

The heat retaining web of the present invention has heat retainingproperties per web thickness which are by about twice higher than thatof the conventional polyester cotton, resin cotton using polyester orfeather and by at least 1.4 times higher than that of conventionalcotton using polyester hollow yarns having relatively high heatretaining properties among the prior art articles.

Since the heat retaining web of the present invention has extremely highheat retaining properties though it is thin, it shows sufficient heatretaining properties even when it is 0.5 to 30 mm thick and, preferably,from 0.5 to 7 mm thick.

The webs forming the heat retaining sheet may be composed of mixed webshaving mutually different average fineness and fineness distributionswithin the range that satisfies the fineness condition of the presentinvention. For example, a heat retaining web having excellent recoveryof compressive elasticity and wash resistance can be obtained by formingthe webs by use of mixed fibers consisting of micro-fibers of a finenessof up to 0.5 d and thick fibers of a fineness of at least 7 d.

Fibers that constitute the webs may be bonded by a third componentbinder such as a low melting polymer in accordance with the intendedapplication of the webs insofar as the softness of the webs is not lost.

In producing the non-woven web of the present invention, it is necessarythat the fibers forming the non-woven web be undrawn yarns. Accordingly,it is advantageous to employ a so-called "melt blow method" such asdisclosed in Japanese Patent Publication No. 22525/1969 in order toproduce the non-woven web of the present invention. FIG. 1 is asectional view showing stepwise the outline of the melt blow productionmethod. A molten polymer stream fed from a polymer charging port 1 of aspinning machine is joined together with a pressurized gas stream at ajoining zone 2, is jetted from an orifice 3, and is then cooled toprovide undrawn fiber yarns 4. When jetted while being accompanied bythe gas stream, the undrawn fiber yarns are mutually separated andbecome independent and are joined together at their mutual contactpoints when cooled. Before they are perfectly solidified, they areperiodically collected on a conveyor 5 to form thin layers 6. These thinlayers 6 are layered like scales to provide the non-woven web 7.

In producing the non-woven web, it is especially preferred to adjust thevariance of weight per unit area of the web, for example, the varianceof weight per square meter for a 5 cm square web, to 5 to 25% in termsof a coefficient of valuation.

FIG. 2 is a perspective view showing an example of the resultingnon-woven web and FIG. 3 is its partial enlarged sectional view. Whilesufficiently independent of and separate from one another, the undrawnfibers 4 entangle with one another and are joined together at the pointsof contact 8, thereby forming the thin layers 6. It can be seen thatthese layers are obliquely deviated from one another, are mutuallylaminated like scales and form the non-woven web 7. FIGS. 4 and 5 arescanning electron micrographs showing the surface condition of theresulting non-woven webs, respectively, at a magnification of 400X and1100X. As is obvious from these micrographs, the fibers forming thenon-woven web have a definite fiber length and are mutually melt-adheredand entangled. Since the present invention uses particularlypolybutylene terephthalate, the spinning temperature can be set at ashigh as 300° C. because the melting point of the polybutyleneterephthalate is 224° C. In comparison with polyethylene terephthalate,therefore, melt-adhesion between the fibers is easier and the shape anddimensional stability of the web can be improved.

When the aforementioned fiber materials, fineness, apparent density,area shrinkage and thermal insulation value are all satisfied, thenon-woven web in accordance with the present invention exhibitsextremely excellent flexibility and heat retaining property, but it isnecessary that the fibers are locally joined so as to leave sufficientgaps between them. The web having such a structure and satisfying theabovementioned various requirements may be formed by integrating aknitted or woven fabric or a heretofore known thin non-woven fabric onone or both surfaces of a non-woven web, as depicted in FIG. 6. Bylaminating other web-like materials, there can be obtained a heatretaining web having a thermal insulation value of 2.0 to 10.0 clo/cm,improving the heat retaining effect and dimensional stability. In FIG.6, reference numerals 9, 10 and 11 represent the knitted fabric, anadhesive layer and a composite web formed by integrally laminating thenon-woven web 5 with the knitted fabric 9, respectively.

The other web-like materials to be laminated on the non-woven web arepreferably 0.05 to 1 mm thick and have sufficient flexibility in thelaminated state and the minimal possible area shrinkage in boilingwater.

It is of course possible to use flame-retarding webs such as aluminumfoil as the abovementioned web-like materials.

It is also possible to change the various properties of the non-wovenweb of the present invention such as hygroscopicity, bulkiness,anti-static properties, hand and the like by blending various knownfibers as the constituent fiber materials in accordance with theintended application while maintaining the heat retaining properties andflexibility of the non-woven web of the invention.

FIGS. 7 and 8 are plan views, each showing an example of clothes usingthe heat retaining web of the present invention. Reference numeral 12represents the portion at which the heat retaining web of the inventionis disposed, and reference numerals 13 and 14 represent coat and pants,respectively. As depicted in the drawings, the heat retaining web of thepresent invention can be adapted to that portion which requires the heatretention because it has not only excellent heat retaining propertiesbut also excellent drapability. It provides excellent heat retaining andenergy-saving effects and an appreciable silhouette.

Next, an elastic heat retaining sheet of the present invention, which issoft and rich in flexibility and has an especially high stretch recoveryratio, will be described.

The elastic heat retaining sheet can be accomplished by a non-woven webwhich is formed by first arranging those elastic fibers independent of,and separate from, one another which consist of a polyether ester typecopolymer containing at least polybutylene terephthalate as a hardsegment and having a substantially undrawn definite fiber length,thereby forming thin fiber layers in which mutual contact points ofthese fibers are joined together by the polyether ester type copolymerper se of the elastomer forming the fibers, and then laminating thesethin fibers, whereby the non-woven web has area shrinkage in boilingwater of up to about 20% and a stretch recovery ratio of at least 50%when stretched by 20%.

Preferred examples of the polyether ester forming the elastic non-wovenweb are elastomers consisting of terephthalic acid, 1,4-butanediol,dicarboxylic acids other than terephthalic acid and/or low-moleculardiols other than 1,4-butanediol and poly(alkylene oxide)glycol having anumber-average molecular weight of about 300 to about 6,000.

In other words, it is an essential requirement that the non-woven webhaving area shrinkage in boiling water of up to about 20% and thestretch recovery ratio of at least 50% when stretched by 20%, asstipulated in the present invention, consists of undrawn fiber filamentscomposed of the abovementioned polyether ester type elastomer and havinga definite fiber length. Only when the non-woven web is formed by theundrawn fiber filaments consisting of the abovementioned polyether estertype elastomer, can there be obtained a non-woven web having the areashrinkage in boiling water of up to 20% and exhibiting the stretchrecovery ratio of at least 50% when stretched by 20%. Even if the fiberconsists of the polyether ester type elastomer, the polyether units asthe elastic segment of the elastomer would be crystallized whenstretched, and this crystallization would lower the elastic recovery ofthe resulting non-woven web. Hence, crystallization of the polyethersegment must be avoided. The term "undrawn fibers" used hereinpreferably refers to undrawn fiber filaments obtained by the spinningmeans such as shown in FIG. 1, but those filaments may also be usedwhich are not perfectly drawn. Hence, the term embraces also semidrawnfiber filaments and those fibers that are once drawn and are thenheat-set under relaxation to exhibit elasticity.

Examples of the dicarboxylic acid component other than terephthalic acidinclude isophthalic acid, phthalic acid, adipic acid and sebacic acidand examples of the diol component other than 1,4-butanediol includeethylene glycol, trimethylene glycol, pentamethylene glycol and thelike. Examples of the poly(alkylene oxide) glycol include polyethyleneglycol, poly(tetramethylene oxide) glycol, poly(1,2-propyleneoxide)glycol and poly(1,3-propylene oxide)glycol. Of them, especiallypreferred is poly(tetramethylene oxide)glycol.

In the elastic non-woven web of the present invention, the fibersconsisting of the abovementioned polyether ester type copolymer aresufficiently independent of, and separate from, one another; that is,they are deposited while sufficiently open, thereby to form thin webs,and the resulting thin webs are layered like scales to form thenon-woven web. In other words, in order to obtain a non-woven fabricwhich is soft and excellent in the stretch recovery ratio, not only thefibers forming the non-woven fabric must be sufficiently independent andseparate but thin layers consisting of the fibers must also be laminatedand layered like scales. According to this scale-like layered structure,the non-woven fabric is capable of sufficiently following up an externalforce and undergoes deformation to give an arbitrary shape.

Since, in the elastic non-woven web in accordance with the presentinvention, the contact points of the constituent fibers are joinedtogether by the fibers themselves, the web can be put to use withoutresort to a third component such as a binder. Thus, the elasticnon-woven web is devoid of such problems as the lack of elasticity,softness and air permeability resulting from the use of a binder.

Since the elastic non-woven web in accordance with the present inventionhas elasticity as compared with the non-woven web consisting ofpolybutylene terephthalate, it does not lose its drapability even whenthe average size ranges from 15 d to 20 d, and has sufficientpracticableness. However, the preferred average size of the fiber is upto 15 d and the fineness is preferably not uniform but distributedwithin the range of about 0.01 to about 20 d.

Besides the aforementioned requirements of the fiber material, areashrinkage in boiling water, stretch recovery ratio and finenessrequirements, the elastic non-woven web in accordance with the presentinvention preferably has an apparent density of 0.1 g/cm³ so that it hasa thermal insulation value of at least 1.5 clo/cm and preferably atleast 1.8 clo/cm. If these requirements are satisfied, there can beobtained a soft heat retaining web that is excellent in both heatretaining properties and elastic recovery ratio.

The elastic non-woven web may be composed of mixed fibers havingmutually different average fineness and mutually different finenessdistributions within the range of the abovementioned finenessrequirements.

The elastic non-woven web of the present invention can be produced bythe melt blow method in the same way as shown in FIG. 1. If necessary,however, the non-woven webs layered like scales on the conveyor may befed to a press roll, are then subjected to predetermined press between apair of hot rolls for integration in order to further strengthenadhesion between the fibers and thus to further improve the stretchrecovery ratio when stretched by 20%.

The shape of the elastic non-woven web of the present invention thusintegrated by the press treatment is substantially the same as thoseshown in FIGS. 2 and 3 except that it is more compact structurally.

Since the heat retaining sheet of the present invention has theconstruction described above, it provides the following excellentfeatures:

(1) peculiar soft feel and tenacity,

(2) thin but having a high heat retaining properties,

(3) free from crease and does not deform,

(4) washable by dry cleaning and laundering,

(5) devoid of inflammability,

(6) highly soft and flexible, and

(7) easily sewn.

Because of these outstanding features, the heat retaining sheet of thepresent invention can be applied to a wide range of applications where athin but highly heat retaining sheet is required or where a light-weightheat retaining sheet is required, such as listed below:

(1) batting for clothing (for jackets, ski wear, golf wear, fishingwear, vests, suits, women's wear, skirts, trousers),

(2) hats,

(3) gloves,

(4) shoes and boots,

(5) cushions and bedclothes,

(6) heat retaining materials for tubes and pipes,

(7) car ceiling and side wall heat retaining materials,

(8) airplane heat retaining materials,

(9) supporters and bandages, and

(10) interlinings.

Hereinafter, the present invention will be described in further detailwith reference to Examples thereof.

In the Examples, the thermal insulation value and the thickness weremeasured in accordance with the following methods.

THERMAL INSULATION VALUE

The heat retaining force of 1 clo means a heat retaining force ofclothes that permits a subject, who reposes in a room, held at 21° C.and up to 50% humidity with an air stream of 10 cm/sec, to keep theaverage skin temperature 33° C. in a comfortable way. It was assumedhere that the subject emitted the heat of 50 kcal/m² ·hour, 75% of whichwas discharged through his clothes. 1 clo was mathematically defined asfollows:

    1 clo=0.18° C.·hour·m.sup.2 /kcal

The measurement was carried out in accordance with ASTM: D-1518-57T.

THICKNESS

The thickness of the non-woven web was measured using a measuring areaof 2 cm² at a 5 g/cm² load.

Hereinafter, the present invention will be described in further detailwith reference to Examples thereof, in which "part or parts" represents"part or parts by weight".

EXAMPLE 1

A microfiber non-woven web consisting of polybutylene terephthalate wasprepared by the melt blow production method.

The non-woven web had an average fineness of 0.2d, an apparent densityof 0.05 g/cm³, a thickness of 4 mm and a weight per unit area of 200g/m². In the web, the fibers were mutually heat-adhered.

The web had a web unevenness value (CV value) of 20%, area shrinkage inboiling water of 7% and a thermal insulation value of 4 clo/cm.

This non-woven web was bonded to a woven fabric by a low-melting powderand was applied to the surface cloth of the back of a vest. Thecomposite material had a thermal insulation value of 5.5 clo/cm. As aresult, the vest fit the body well, was devoid of the feel of batting,exhibited excellent heat retaining properties and could be usedeffectively as a heat retaining material.

Though used for an extended period, the vest withstood repetitivewashing and no decrease in the heat retaining properties were observed.

EXAMPLE 2

A non-woven web of microfibers consisting of polybutylene terephthalatewas prepared by the melt blow production method in such a manner thatadhesion between the fibers was increased by shortening the collectingdistance between inlet and conveyor. The non-woven web had an averagefineness of 0.1d, a thickness of 2.5 mm, a weight per unit area of 120g/m² and an apparent density of 0.048 g/cm³. The web unevenness (CVvalue) was 12%, the area shrinkage in boiling water was 8% and thethermal insulation value was 3.5 clo/cm.

This non-woven web was bonded to a thin fabric to form a compositematerial for the surface cloth of the back of a sack suit. As a result,the heat retaining properties of the suit were improved withoutdeteriorating its appearance.

Though used for an extended period, the suit withstood repetitivewashing and maintained the heat retaining properties. The thermalinsulation value of the composite material was 4.6 clo/cm.

EXAMPLE 3

A non-woven web consisting of polybutylene terephthalate was prepared bythe melt blow production method.

The non-woven web had an average fineness of 0.2d, a thickness of 7 mm,a weight per unit area of 200 g/m² and an apparent density of 0.029g/cm³. In the non-woven web, the fibers were mutually heat-adhered.

The web unevenness (CV value) was 18%, the area shrinkage in boilingwater was 10% and the thermal insulation value was 1.9 clo/cm.

This non-woven web was bonded to a woven fabric and was fitted to thewaist of pants. The composite material had the thermal insulation valueof 3.2 clo/cm. As a result, the pants fit well, were devoid of anychange in appearance and exhibited excellent heat retaining properties.

The parts had good durability and no decrease in the heat retainingproperties were observed over an extended period.

EXAMPLE 4

A non-woven web consisting of polybutylene terephthalate and having anaverage fineness of 0.2d was prepared by the melt blow productionmethod. This web had a weight per unit area of 200 g/cm², a thickness of6 mm, an apparent density of 0.033 g/cm³, area shrinkage in boilingwater of 7.5% and a thermal insulation value of 3.2 clo/cm.

Short fiber polyester non-woven fabrics having a weight per unit area of20 g/m² were laminated on both sides of this non-woven web and were thenpressed, thereby providing a composite material. Though no binder wasused in this composite material, it was formed integrally and its washshrinkage ratio was 1.5%. The wash resistance could thus be improvedmarkedly as compared with the wash shrinkage ratio of 10% when thenon-woven fabrics were not laminated. Incidentally, the wash shrinkageratio of the short fiber polyester non-woven fabrics was 1.0%.

EXAMPLE 5

A non-woven web was prepared by the melt blow production method using acopolymer obtained by copolymerizing polybutylene terephthalate with 3%by weight of isophthalic acid. This non-woven web has an averagefineness of 0.2d, a thickness of 4 mm, a weight per unit area of 200g/m², an apparent density of 0.05 g/cm³, area shrinkage in boiling waterof 8% and a thermal insulation value of 4.1 clo/cm.

EXAMPLE 6

A non-woven web consisting of mixed fibers (mixing ratio: 60% of fibersof an average fineness of 0.3 d and 40% of fibers of an average finenessof 8d) of polybutylene terephthalate having the average fineness of 0.3dand 8d was prepared by the melt blow production method. This non-wovenweb had a weight per unit area of 200 g/m², a thickness of 12 mm, anapparent density of 0.017 g/cm³, area shrinkage in boiling water of 6%and a thermal insulation value of 1.3 clo/cm. Incidentally, the twosizes of fibers were obtained mainly by changing diameters of a spinningorifice.

Since this non-woven web incorporated polybutylene terephthalate fibershaving a greater average fineness (8d) in comparison with the non-wovenweb consisting of polybutylene terephthalate of an average fineness of0.3d alone, it was excellent in recovery of compressive elasticity andcould retain the initial thickness even after used for an extendedperiod. In addition, decrease in heat retaining properties did notoccur.

EXAMPLE 7

In preparing a non-woven web consisting of polybutylene terephthalateand having an average fineness of 0.3d by the melt below productionmethod, about 2% by weight, based on the web weight, of an atomizedadhesive consisting of an acrylic resin was sprayed onto the web toobtain a non-woven web having enhanced adhesion between the fibers.

The resulting web had a weight per unit of 160 g/m², a thickness of 10mm, an apparent density of 0.016 g/cm³, area shrinkage in boiling waterof 3% and excellent dimensional stability. Even when washed, the webexhibited very little shrinkage.

EXAMPLE 8

A polyether ester copolymer obtained by polymerizing 28 parts ofdimethyl terephthalate, 12 parts of dimethyl phthalate, 33 parts ofpoly(tetramethylene oxide)glycol having a number-average molecularweight of about 1,000 and 27 parts of 1,4-butanediol was employed toprepare fibers in the same way as in Example 1. The resulting fibershaving an average fineness of 8d (0.3 to 13d) were collected on aconveyor to obtain an elastic non-woven web.

This non-woven web had a weight per unit area of 200 g/m² and anapparent density of 0.05 g/cm³. The constituent fibers were self-bondedat the points of contact of the fibers.

The non-woven web had area shrinkage in boiling water of 8% and arecovery ratio of 71% when stretched by 20%. The thermal insulationvalue of the web was 3.8 clo/cm.

When the web of the present invention was used as batting in ski pants,it had heat retaining properties comparable to that of ordinary battingand was soft and excellent in elastic recovery. In addition, the pantswore well at the knees.

EXAMPLE 9

A polyether ester copolymer obtained by polymerizing 35 parts ofdimethyl terephthalate, 15 parts of dimethyl isophthalate, 15 parts ofpoly(tetramethylene oxide)glycol having a number-average molecularweight of about 1,000 and 35 parts of 1,4-butanediol was employed toproduce fibers by the melt blow production method. The resulting fiberswere collected on a conveyor to obtain an elastic non-woven web. In thiscase, the distance between the inlet and the conveyor was set to 30 cmto collect the fibers.

The average fineness of the elastic fibers forming the non-woven web was10d (0.5-15d) and the points of contact between the fibers were joinedby self-adhesion of the fibers themselves. The non-woven web has aweight per unit area of 50 g/m², a recovery ratio of 82% when stretchedby 20% and area shrinkage in boiling water was 7.5%.

The non-woven web was passed through a hot roll heated to 170° C. tofurther strengthen mutual adhesion of the fibers. As a result, therecovery ratio when stretched by 20% could be improved to 90%.

EXAMPLE 10

A polymer obtained by adding 5 parts of polybutylene terephthalate as anucleating agent to 100 parts of the copolymer used in Example 9 wasemployed to produce fibers by the melt below production method. Therewas thus obtained a non-woven web consisting of the fibers having anaverage fineness of 12d.

This web had a weight per unit area of 50 g/m², area shrinkage byboiling water of 7.5% and a stretch recovery ratio of 85% when stretchedby 20%.

Needle-punched non-woven fabrics were laminated to this web and wereheat-adhered. The resulting non-woven web had a small drop in thestretch recovery ratio due to the lamination of the needle-punchednon-woven fabrics and was rich in elastic recovery and softness.

What is claimed is:
 1. A heat retaining sheet comprising a web formed bymutually bonding fibers containing polybutylene terephthalate, saidfibers having a definite fiber length, being substantially undrawn andsubstantially uncrimped and having an average fineness of up to about 15denier and a fineness distribution ranging from 0.001 to 40 denier, saidweb having area shrinkage in boiling weter of up to about 20%.
 2. Theheat retaining sheet as defined in claim 1 wherein said fibers consistessentially of polybutylene terephthalate.
 3. The heat retaining sheetas defined in claim 1 wherein said fibers consist essentially ofcopolymeric polybutylene terephthalate.
 4. The heat retaining sheet asdefined in claim 1 wherein said web has an apparent density of up toabout 0.1 g/cm³.
 5. The heat retaining sheet as defined in claim 1wherein said webs have a thermal insulation value of at least 1.8clo/cm.
 6. The heat retaining sheet as defined in claim 1 wherein saidfibers having a definite fiber length have an average fineness of up toabout 0.5 deniers.
 7. The heat retaining sheet as defined in claim 1,comprising at least a web in which fibers having an average size of upto about 0.5 deniers are mutually bonded and which has area shrinkage byboiling water of up to about 20% and an apparent density of up to about0.1 g/cm³, said heat retaining sheet having a thermal insulation valueof at least 1.8 clo/cm.
 8. The heat retaining sheet as defined in claim6 wherein said fibers having a definite fiber length have an averagefineness of 0.03 to 0.5 deniers and a fineness distribution of 0.01 to 1denier.
 9. The heat retaining sheet as defined in claim 1 wherein saidfibers having a definite fiber length have mutually different averagefineness and fineness distributions.
 10. The heat retaining sheet asdefined in claim 4 wherein said web has an apparent density of 0.01 to0.1 g/cm³.
 11. The heat retaining sheet as defined in claim 1 wherein atleast one another web is layered on, and integrated with, one or bothsurfaces of said web.
 12. The heat retaining sheet as defined in claim11 wherein said layered web is other non-woven fabrics.
 13. The heatretaining sheet as defined in claim 11 wherein said layered web is wovenfabric.
 14. The heat retaining sheet as defined in claim 11 wherein saidlayered web is flame-retarding web.
 15. The heat retaining sheet asdefined in claim 1 wherein said web is 0.5 to 30 mm thick.
 16. The heatretaining sheet as defined in claim 11 wherein said other web is 0.05 to1 mm thick.
 17. The heat retaining sheet as defined in claim 3 whereinsaid copolymer component is at least one member selected from the groupconsisting of isophthalic acid, adipic acid, sebacic acid and phthalicacid.
 18. The heat retaining sheet as defined in claim 1 wherein saidfibers having a definite fiber length are an elastomer consisting of apolyether ester type copolymer having butylene terephthalate as the hardsegment.
 19. The heat retaining sheet as defined in claim 18 whereinsaid fibers having a definite fiber length are an elastomer consistingof terephthalic acid, 1,4-butanediol, a dicarboxylic acid other thanterephthalic acid and/or a low-molecular diol other than 1,4-butanedioland poly(alkylene oxide)glycol having a number-average molecular weightof about 300 to 6,000.
 20. The heat retaining sheet as defined in claim19 wherein said dicarboxylic acid other than terephthalic acid is onemember selected from the group consisting of isophthalic acid, phthalicacid, adipic acid and sebacic acid.
 21. The heat retaining sheet asdefined in claim 19 wherein said diol other than 1,4-butanediol is onemember selected from the group consisting of ethylene glycol,trimethylene glycol and pentamethylene glycol.
 22. The heat retainingsheet as defined in claim 21 wherein said poly(alkylene oxide)glycol isone member selected from the group consisting of polyethylene glycol,poly(tetramethylene oxide)glycol, poly(1,2-propylene oxide)glycol andpoly(1,3-propylene oxide)glycol.
 23. The heat retaining sheet as definedin claim 18 wherein said fibers having a definite fiber length have anaverage fineness of up to about 20 deniers.
 24. The heat retaining sheetas defined in claim 23 wherein said fibers having a definite fiberlength have an average fineness of up to 15 deniers and a finenessdistribution of 0.01 to 20 deniers.
 25. The heat retaining sheet asdefined in claim 24 wherein said fibers having a definite fiber lengthhave mutually different average fineness and mutually different finenessdistributions.
 26. The heat retaining sheet as defined in claim 18wherein said web has a strength recovery ratio of at least 50% whenstretched by 20%.
 27. The heat retaining sheet as defined in claim 26wherein said web has an apparent density of up to about 0.1 g/cm³. 28.The heat retaining sheet as defined in claim 27 wherein said web has athermal insulation value of at least 1.5 clo/cm.
 29. An elastic heatretaining sheet comprising a non-woven web formed from thin fiber layerslaminated together, wherein said thin fiber layers comprise mutuallybonded elastic fibers layered sufficiently independent and separate withrespect to one another, wherein said elastic fibers consist essentiallyof an elastomer of a polyether ester type copolymer containing butyleneterephthalate as the hard segment and have an average fineness up toabout 15 denier and a fineness distribution of 0.01 to 20 denier andwherein said elastic heat retaining sheet has a stretch recovery ratioof at least 50% when stretched 20%.
 30. The elastic heat retaining webas defined in claim 29 wherein an apparent density is up to 0.1 g/cm³and a thermal insulation value is at least 1.5 clo/cm.
 31. A heatretaining sheet as defined in claim 7 wherein said fibers having adefinite fiber length have an average fineness of 0.03 to 0.5 denier anda fineness distribution of 0.01 to 1 denier.
 32. The heat retainingsheet as defined in claim 7 wherein said web has an apparent density of0.01 to 0.1 g/cm³.